I have the Sobel Edge detection gem working, but I want to make a change: As is, if you're looking nearly parallel to a long plane, you'll see a black patch stretching across it. I can change the minimum intensity and contrast to give a gradation to that black line, but it's still there. What I want to do is to skip drawing the black altogether if the dot product of the surface normal with the camera direction (like what Fresnel node does) is above a certain threshold. The problem is that I can't figure out how to get the normal of individual pixels. How would I do that?
